Composite structures are gaining more and more useage in modern aircraft, automobiles and other devices where lightweight parts of high strength are desired. These applications are feasible because of the high mechanical strength and machinability associated with composite parts, particularly those manufactured from graphite epoxy mixtures. Testing has shown that in many applications graphite epoxy parts are substantially stronger and more reliable than comparable metal parts.
In view of the above, there is increasing interest in efficient manufacture of such composite parts. One method of manufacturing complex composite designs is through the use of graphite epoxy tape (i.e., structural tape) which is positioned on a basic structure and then cured to form a high strength finished part which can be machined as desired.
Composite parts are most frequently used for aircraft components; close inspection of aircraft wings and tails reveals that even the largest of such aircraft components are comprised of many small details. As a result, it is rarely possible to lay straight lengths of structural tape greater than three feet. Since multiple layers of tape are often required, and aircraft components require a great many pieces of tape due to the short tape course length, hand laying of such individual aircraft components is a long labor intensive job.
Machines have therefore been developed to automatically lay tape to form composite structures. An example of an automatic tape laying machine can be found in U.S. Pat No. 3,810,805 to Goldsworthy et al. The tape laying machine disclosed in the Goldsworthy patent is a straight forward device which is useful to review when considering the problems encountered during use of automated tape laying machines.
The Goldsworthy machine uses conventional three inch wide tape to laminate an underlying structure. Use of such wide tape makes it very difficult to properly laminate parts having small details. Therefore, required details would have to be added or machined onto the part after lamination. In addition to obscuring details, use of wide tape produces a great deal of unuseable scrap tape pieces and makes it difficult to accurately orient the tapehead to follow part contour.
A second problem with this conventional tape machine is that after each single layer of tape is applied, the tape laying head must either be retracted and returned to an arbitrary initiation point or rotated 180.degree. and indexed. As a result, a great deal of time is lost indexing and orienting the tapehead rather than actually laying tape. In such devices, up to two-thirds of machine operation time is spent in non-tape laying operations. Further, minor orientation errors which result in overlaps or gaps between adjacent tape layers are more likely after reorientation and indexing.
Finally, another consideration is the massive nature of the Goldsworthy device. This device calls for a great deal of components to be installed on the movable tape head. Head positioning therefore requires heavy duty actuators and motors. The massiviness of such a device mitigates against rapid and efficient movement of the tape laying head.
In view of the above it is an object of this invention to provide an automatic tape laying machine having a lightweight tape laying head arranged to reduce machine time spent in non-tape laying operations.
Further, it is an object of this invention to provide a tape laying machine that is capable of increased flexibility of orientation to the various contours required for tape laying on complex composite parts.
Finally, it is an object of the present invention to provide a tape laying machine that is capable of accurately laying strips of tape while minimizing overlaps, gaps, and tape wastage.